An official website of the United States government
Highly concentrated aqueous electrolytes (termed water-in-salt electrolytes, WiSEs) at solid-liquid interfaces are ubiquitous in myriad applications including biological signaling, electrosynthesis, and energy storage. This interface, known as the electrical double layer (EDL), has a different structure in WiSEs than in dilute electrolytes. Here, we investigate how divalent salts [zinc bis(trifluoromethylsulfonyl)imide, Zn(TFSI)2], as well as mixtures of mono- and divalent salts [lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) mixed with Zn(TFSI)2], affect the short- and long-range structure of the EDL under confinement using a multimodal combination of scattering, spectroscopy, and surface forces measurements. Raman spectroscopy of bulk electrolytes suggests that the cation is closely associated with the anion regardless of valency. Wide-angle X-ray scattering reveals that all bulk electrolytes form ion clusters; however, the clusters are suppressed with increasing concentration of the divalent ion. To probe the EDL under confinement, we use a Surface Forces Apparatus and demonstrate that the thickness of the adsorbed layer of ions at the interface grows with increasing divalent ion concentration. Multiple interfacial layers form following this adlayer; their thicknesses appear dependent on anion size, rather than cation. Importantly, all electrolytes exhibit very long electrostatic decay lengths that are insensitive to valency. It is likely that in the WiSE regime, electrostatic screening is mediated by the formation of ion clusters rather than individual well-solvated ions. This work contributes to understanding the structure and charge-neutralization mechanism in this class of electrolytes and the interfacial behavior of mixed-electrolyte systems encountered in electrochemistry and biology.
more »
« less
A Systematic Electrochemical Investigation of a Dimethylamine Cosolvent-Assisted Nonaqueous Zinc(II) Bis(trifluoromethylsulfonyl)imide Electrolyte
The development of the multivalent electrolytes is a critical component to advance polyvalent energy storage technology. In this work, a new and simple nonaqueous zinc electrolyte is developed and investigated where a secondary amine is introduced as a cosolvent. The addition of dimethylamine (DMA) as a cosolvent in THF facilitates the solubilization of Zinc (II) bis(trifluoromethanesulfonyl)imde (Zn(TFSI)2) and results in a homogeneous electrolyte with reversible plating of zinc achieved at high coulombic efficiencies. The electrochemical properties of the developed electrolyte and the effects of the cosolvent and salt concentrations are systematically investigated. It was found that increasing the ratio of the cosolvent DMA in THF for a Zn(TFSI)2electrolyte leads to more facile kinetics, better ion solubilization, and higher ion mobility evidenced by up a significant increase in conductivity as well as the plating/stripping current densities. Increased Zn(TFSI)2salt concentration in a 2.0 M DMA in THF solvent mixture not only leads to a higher current density and conductivity, but also a higher molar conductivity due to a redissociation mechanism. The findings in this study are relevant and important to further understand and characterize multivalent electrolytes from a simple and effective electrolyte design strategy.
more »
« less
- Award ID(s):
- 1919919
- PAR ID:
- 10361665
- Publisher / Repository:
- The Electrochemical Society
- Date Published:
- Journal Name:
- Journal of The Electrochemical Society
- Volume:
- 168
- Issue:
- 3
- ISSN:
- 0013-4651
- Page Range / eLocation ID:
- Article No. 030516
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Aqueous zinc‐ion batteries are promising alternatives to lithium‐ion batteries due to their cost‐effectiveness and improved safety. However, several challenges, including corrosion, dendrites, and water decomposition at the Zn anode, hinder their performance. Herein, an approach is proposed, that deviates from the conventional design by adding water into a propylene carbonate‐based organic electrolyte to prepare a non‐flammable “water‐in‐organic” electrolyte. The chaotropic salt Zn(ClO4)2exploits the Hofmeister effect to promote the miscibility of immiscible liquid phases. Interactions between propylene carbonate and water restrict water activity and mitigate unfavorable reactions. This electrolyte facilitates preferential Zn (002) deposition and the formation of solid electrolyte interphase. Consequently, the “water‐in‐organic” electrolyte achieves a 99.5% Coulombic efficiency at 1 mA cm−2over 1000 cycles in Zn/Cu cells, and constant cycling over 1000 h in Zn/Zn symmetric cells. A Na0.33V2O5/Zn battery exhibits impressive cycling stability with a capacity of 175 mAh g−1for 800 cycles at 2 A g−1. Additionally, this electrolyte enables sustainable cycling across a wide temperature range from −20 to 50 °C. The design of a “water‐in‐organic” electrolyte employing a chaotropic salt presents a potential strategy for high‐performance electrolytes in zinc‐ion batteries with a large stability window and a wide temperature range.more » « less
-
Abstract Aqueous zinc-ion batteries, in terms of integration with high safety, environmental benignity, and low cost, have attracted much attention for powering electronic devices and storage systems. However, the interface instability issues at the Zn anode caused by detrimental side reactions such as dendrite growth, hydrogen evolution, and metal corrosion at the solid (anode)/liquid (electrolyte) interface impede their practical applications in the fields requiring long-term performance persistence. Despite the rapid progress in suppressing the side reactions at the materials interface, the mechanism of ion storage and dendrite formation in practical aqueous zinc-ion batteries with dual-cation aqueous electrolytes is still unclear. Herein, we design an interface material consisting of forest-like three-dimensional zinc-copper alloy with engineered surfaces to explore the Zn plating/stripping mode in dual-cation electrolytes. The three-dimensional nanostructured surface of zinc-copper alloy is demonstrated to be in favor of effectively regulating the reaction kinetics of Zn plating/stripping processes. The developed interface materials suppress the dendrite growth on the anode surface towards high-performance persistent aqueous zinc-ion batteries in the aqueous electrolytes containing single and dual cations. This work remarkably enhances the fundamental understanding of dual-cation intercalation chemistry in aqueous electrochemical systems and provides a guide for exploring high-performance aqueous zinc-ion batteries and beyond.more » « less
-
Abstract It remains a challenge to design aqueous electrolytes to secure the complete reversibility of zinc metal anodes. The concentrated water‐in‐salt electrolytes, e.g., 30 m ZnCl2, are promising candidates to address the challenges of the Zn metal anode. However, the pure 30 m ZnCl2electrolyte fails to deliver a smooth surface morphology and a practically relevant Coulombic efficiency. Herein, it is reported that a small concentration of vanillin, 5 mg mLwater−1, added to 30 m ZnCl2transforms the reversibility of Zn metal anode by eliminating dendrites, lowering the Hammett acidity, and forming an effective solid electrolyte interphase. The presence of vanillin in the electrolyte enables the Zn metal anode to exhibit a high Coulombic efficiency of 99.34% at a low current density of 0.2 mA cm−2, at which the impacts of the hydrogen evolution reaction are allowed to play out. Using this new electrolyte, a full cell Zn metal battery with an anode/cathode capacity (N/P) ratio of 2:1 demonstrates no capacity fading over 800 cycles.more » « less
-
Robust multivalent ion interaction in electrodes is a grand challenge of next-generation battery research. In this manuscript, we design molecularly-precise nanographene cathodes that are coupled with metallic Zn anodes to create a new class of Zn-ion batteries. Our results indicate that while electrodes with graphite or flat nanographenes do not support Zn-ion intercalation, the larger intermolecular spacing in a twisted peropyrene enables peropyrene electrodes to facilitate reversible Zn-ion intercalation in an acetonitrile electrolyte. While most previous Zn-ion batteries utilize aqueous electrolytes, the finding that nonaqueous Zn electrolytes can support intercalation in nanographenes is important for expanding the design space of nonaqueous multivalent batteries, which often possess higher voltages than their aqueous counterparts. Furthermore, because these nanographenes can be synthesized using a bottom-up approach via alkyne benzannulation, this work paves the way for future battery electrodes that contain other molecularly-precise nanographenes with tailored electrochemical properties.more » « less
